Hadoop学习笔记（一）之示例程序：计算每年的最高温度MaxTemperature

package testMapReduce;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class TestTemperature {
public static class dataMapper extends Mapper<LongWritable,Text,Text,IntWritable>{
private static final int MISSING=9999;

public void map(LongWritable key,Text value,Context context)throws IOException,InterruptedException{

String line=value.toString();
String year=line.substring(15,19);
int airTemperature;
if(line.charAt(87) == '+'){
airTemperature= Integer.parseInt(line.substring(88, 92));
}else{
airTemperature=Integer.parseInt(line.substring(87,92));
}
String quality=line.substring(92,93);
if(airTemperature!=MISSING&&quality.matches("[01459]")){
context.write(new Text(year), new IntWritable(airTemperature));
}
}
}

public static class dataReducer extends Reducer<Text,IntWritable,Text,IntWritable>{
public void reduce(Text key,Iterable<IntWritable> values,Context context)throws IOException,InterruptedException{
int maxValue=Integer.MIN_VALUE;
for(IntWritable value:values)	{
maxValue= Math.max(maxValue, value.get());
}
context.write(key, new IntWritable(maxValue));
}

}

public static void main(String args[])throws Exception{
Configuration conf=new Configuration();
if(args.length!=2){
System.err.println("missing in or out");
System.exit(2);
}
Job job=new Job(conf,"TestTemperature");
job.setJarByClass(TestTemperature.class);
job.setMapperClass(dataMapper.class);
job.setReducerClass(dataReducer.class);
job.setCombinerClass(dataReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job,new Path(args[1]));
System.exit(job.waitForCompletion(true)?0:1);

}
}